Electric-discharge lamp lighting device and lighting fixture

ABSTRACT

An electric-discharge lamp lightning device includes a first frequency controller for sweeping a switching frequency so that the output of an inverter is gradually increased in order to allow an electric-discharge lamp to be started and lighted, and a second frequency controller for detecting the output power of the inverter by a current flowing in a resonant circuit and controlling the switching frequency so that the output power is set to be a target value after the discharge lamp is started and lighted. The first frequency controller includes a holding means for holding the switching frequency just after the lighting detection when the output power is smaller than the target value at the lighting detection of the electric-discharge lamp by a lighting detection circuit.

TECHNICAL FIELD

The present invention relates to an electric-discharge lamp lightingdevice and a lighting fixture using the electric-discharge lamp lightingdevice.

BACKGROUND ART

FIG. 1 is a diagram showing a configuration of a conventionalelectric-discharge lamp lighting device. This electric-discharge lamplighting device includes a dc power supply 1 for outputting a dc voltageVDC by receiving a electric power from an ac power supply Vin, aninverter 2 for outputting a high-frequency voltage Vcoil by receiving aelectric power from the dc power supply 1, a voltage controller 13 forcontrolling variability of the output voltage Vcoil from the inverter 2by controlling a switching frequency of the inverter 2, a load 3including an induction coil 5 connected to an output of the inverter 2and an electrodeless discharge lamp 6 provided adjacent to the inductioncoil 5, and a current controller 17 for controlling the switchingfrequency so as to maintain an output power of the electrodelessdischarge lamp 6 at an approximately constant target value.

The dc power supply 1 includes a rectifier diode bridge DB and a boostchopper circuit including a switching element Q6, an inductor L10, adiode D10, a controller 10, and a smoothing capacitor C10. The inverter2 includes switching elements Q3 and Q4, and an inductor Ls andcapacitors Cp and Cs that are elements of a resonant circuit. Theelectrodeless discharge lamp 6 includes a clear spherical glass bulb ora spherical glass bulb of which an inner surface is coated withphosphor, filled with discharge gas such as inactive gases and metalvapor (for instance, mercury and rare gases). The induction coil 5 isprovided adjacent to the electrodeless discharge lamp 6. The inverter 2applies a high-frequency current of several tens of kHz to several MHzto the induction coil 5, whereby a high-frequency electromagnetic fieldis produced by the induction coil 5 and a high-frequency power issupplied to the electrodeless discharge lamp 6. According to this, ahigh-frequency plasma current is produced in the electrodeless dischargelamp 6 so as to produce ultraviolet or visible light.

As shown in FIG. 2, a drive circuit 11 includes a constant voltagesource Es, a voltage control oscillator VCO, and resistors R10 and R11.An input terminal VI of the voltage control oscillator VCO is suppliedwith an output voltage of the constant voltage source Es divided by theresistors R10 and R11, whereby an oscillation frequency is alteredaccording to a sink current Io from the respective dividing points. Theinput terminal VI of the voltage control oscillator VCO is supplied witha voltage depending on the sink current Io, and the voltage controloscillator VCO outputs an approximate square wave drive signal, at aswitching frequency finv corresponding to the voltage depending on thesink current Io, with respect to each switching element Q3 and Q4mutually shifted in phase by approximately 180° between an Hout terminaland an H-GND terminal and between an Lout terminal and an L-GNDterminal.

The voltage controller 13 includes an integrator including anoperational amplifier Q1, a resistor R1, and a capacitor C1, a switchSW0 for discharging a charge of the capacitor C1, and the like.

The current controller 17 includes an integrator including anoperational amplifier Q9, a resistor R10, and a capacitor C11, resistorsR5 and R6 for producing a reference voltage, and the like. The currentcontroller 17 differentially amplifies a signal from a resistor Rd fordetecting a resonance current of the inverter 2.

The drive circuit 11 varies the switching frequency according to a sum(=Io) of sink currents Isw, Ifb and Ivr flowing into the voltagecontroller 13, the current controller 17 and a variable resistor VR fromthe input terminal VI.

Variable resistor VR is performed to absorb deviations in circuitcomponents, such as the resonant circuit of the inverter 2 and load 3,and the drive circuit 11. When a frequency sweep control (describedlater) is performed by the voltage controller 13, the variable resistorVR is adjusted for setting an appropriate frequency variation rangethereby performing a stable starting and lighting. The following aredescriptions of operations with reference to FIGS. 4 and 7. Note that,in FIGS. 4 and 7, a reference sign “a” (solid line) represents a casewith a variation of a load impedance, and a reference sign “b” (dashedline) represents a case with no variation of the load impedance. Whenthe switch SW0 is switched from an ON-state to an OFF-state, the voltagecontroller 13 charges the capacitor C1 by supplying a electric powerfrom a dc voltage E1 via the resistor R1, applies a voltage VC1 at bothends of the capacitor C1 to a non-inverting input terminal of theoperational amplifier Q1, and varies the voltage VI according to thevoltage VC1 at both ends of the capacitor C1, so as to perform thefrequency sweep control (start frequency fs→end frequency fe) of thedrive circuit 11.

When it is assumed here that the relationship between the input voltageVI and switching frequency finv of the drive circuit 11 is set to havean inclination shown in FIG. 3, the voltage VI is increased since thesink current Io (=Isw) is decreased when the voltage VC1 is increased.As a result, the switching frequency finv is gradually decreased.Therefore, the voltage Vcoil is gradually increased when the switchingfrequency finv and the voltage Vcoil have a relationship shown in FIG.7. In addition, since the electrodeless discharge lamp 6 is configuredto exceed a voltage minimally necessary to start ignition during thefrequency sweep, the electrodeless discharge lamp 6 is lighted at acertain switching frequency finv (=fi), and the voltage Vcoil isdecreased immediately, thereby shifting to the lighting side on thecurve line in the figure.

Note that, during the frequency sweep control, the resonance current ofthe inverter 2 is increased from an initial state (≅zero). Thus, anoutput of the operational amplifier Q9 is decreased from the highvoltage at the initial state. However, the operational amplifier Q9produces a delay time to an operation of a differential amplifier due tothe function of the resistor R10 and the capacitor C11 of theintegrator. Therefore, while the output Vout of the operationalamplifier Q9 is high compared with the voltage VI of the input terminalof the drive circuit 11, the sink current Ifb from the drive circuit 11becomes approximately zero and a mask operation is performed, therebyresulting in the current Io≅Isw+Ivr. Accordingly, the switchingfrequency of the drive circuit 11 is controlled by the output of thevoltage controller 13.

Then, after the electrodeless discharge lamp 6 is lighted at the timet=t2, the switching frequency keeps varying until the voltage VC1becomes a constant value. In this case, after the electrodelessdischarge lamp 6 is lighted when the switching frequency is “fi” in FIG.7, the switching frequency keeps varying until the end point of thefrequency, “fe”. However, the operational amplifier Q9 performs anegative feedback operation thereby the current Ifb flows out at thetime t>t3 due to the decrease of the output Vout of the operationalamplifier Q9. Then the switching frequency finv is increased, and thefrequency is controlled until resulting in a predetermined resonancecurrent of the inverter 2 arranged according to a reference voltagedetermined by the resistors R5 and R6, thereby resulting in a certainfrequency fx. Due to such a feedback control, it is possible to maintainthe output power of the inverter 2 at an approximately constantpredetermined value.

In addition, as shown in FIG. 12, the load 3 may be otherelectric-discharge lamps such as a construction including anelectric-discharge lamp (fluorescent light) FL having filaments F1 andF2 and a capacitor C20, and the like. Such electric-discharge lampsperform the similar operations.

In particular, the load of the electrodeless discharge lamp is aninductor load when starting ignition. Thus, a larger voltage and poweris required when starting compared with other light sources such as afluorescent light with electrodes. Accordingly, it is necessary to set aQ factor of the resonant circuit of the inverter 2 to be high in orderto start and light stably. However, when there are some factors for aload impedance variation of the inverter 2 such as a change in ambienttemperature and an approach of a metal housing toward a circumference ofthe electrodeless discharge lamp 6, the voltage Vcoil is greatlyaltered, which results in difficulty in starting and lighting stably.Therefore, by starting by the frequency sweep, it is possible to startand light stably since an influence of the load impedance variation canbe absorbed to some extent. Consequently, starting by the frequencysweep can be effective especially when the electrodeless discharge lampis employed.

Japanese Patent Laid-Open Publication No. 2005-063862 discloses astart-up of a load of an electrodeless discharge lamp using frequencysweep, and discloses a configuration to improve start-up performance byapplying a sufficient voltage even if constants of components arealtered by sweeping from a higher frequency than an actual resonancefrequency toward the resonance frequency.

However, when the inverter 2 and the load 3 include the resonantcircuit, and when the electric-discharge lamp is started and lightedbeing supplied with power by the switching frequency control by use ofthe resonance property, a resonance output of the resonant circuitincluded in the inverter 2 and the load 3 varies as an impedances of theinverter 2 and the load 3 vary. Thus, there was a problem that a stablestarting and lighting could not be achieved because of an insufficientpower supply to the electric-discharge lamp, an occurrence of dying out,and the like. As for factors for such impedance variation, a change inambient temperature, a variability and time-dependent change ofconstants of circuit components, an approach of a metal housing towardthe load 3, and the like are included.

Specifically, when the electrodeless discharge lamp 6 is uses as theload 3, the impedance variation is significantly occurred because of theapproach of the metal housing. FIG. 6 shows an example of a downlightusing the electrodeless discharge lamp 6. The electrodeless dischargelamp 6 in the downlight is covered with a reflecting plate 30. When thereflecting plate 30 has high conductivity especially being made ofmetal, an induced current 31 by electromagnetic induction from theinduction coil 5 circularly flows on the reflecting plate 30. Thus, aninductive component by the reflecting plate 30 is produced, whichresults in a parallel connection of the inductor to the induction coil 5in an equivalent circuit. Consequently, the resonance curve lines whenstarting and lighting as shown in FIG. 7 are shifted to the highfrequency side compared with a case not including the metal housing suchas a downlight.

In the case with the variation of the load impedance in FIG. 7 (shown asthe solid line, the reference sign “a”), the frequency varies until thecapacitor C1 is fully charged and the voltage VC1 becomes the constantvalue even after the electrodeless discharge lamp 6 is lighted.Therefore, the frequency varies until the end point frequency fe.However, since the resonance curve line is shifted to the high frequencyside, the frequency sweep is performed until over a peak of theresonance curve line when lighting and further until an area where theoutput voltage Vcoil is decreased. Thus, the end point frequency feresults in a lower frequency than the peak of the resonance curve linewhen lighting. In such an area, the switching frequency control by anegative feedback operation using the operational amplifier Q9 of thecurrent controller 17 is to be unable to function because of an increaseand decrease relationship between the switching frequency and the outputpower (or the resonance current of the inverter 2). As a result, therewere problems such as that the output power could not become apredetermined value, and the electrodeless discharge lamp 6 was dyingout.

As a method to avoid such a matter, it may be applicable that the endpoint frequency fe is adjusted while the electrodeless discharge lamp 6is fixed to an apparatus surrounded by the metal housing. However, it isnecessary to perform such adjustment for each case in order to adapt toa variety of apparatuses. This is not substantive because of much timeand high cost.

The present invention has been made to solve the above-mentionedproblem. It is an object of the present invention to provide anelectric-discharge lamp lighting device and a lighting fixture thereofcapable of starting and lighting stably even when a load impedance ofthe discharge lamp varies.

SUMMARY OF THE INVENTION

In order to solve the above-described problems, an electric-dischargelamp lighting device according to an aspect of the present invention, asshown in FIG. 8, includes: a power inverter (inverter 2) for outputtingan ac voltage Vcoil by receiving a electric power from a dc power supply1 and includes at least switching elements Q3 and Q4 and a resonantcircuit (Ls, Cp, Cs); a drive circuit 11 for driving the switchingelements Q3 and Q4; a load 3 connected to an output of the powerinverter and connected to at least an electric-discharge lamp 6; a firstfrequency controller 13 for sweeping an switching frequency finv of thedrive circuit 11 so that the output of the power inverter is graduallyincreased in order to allow the electric-discharge lamp 6 to be startedand lighted; a second frequency controller 17 for detecting an outputpower of the power inverter by a current flowing in the resonant circuitand controlling the switching frequency of the drive circuit 11 so thatthe output power is set to be a target value after the discharge lamp 6is started and lighted; and a lighting detection circuit 14 performing alighting detection of the electric-discharge lamp 6 by detecting theoutput of the power inverter, wherein the first frequency controller 13includes a holding means 16 for holding an switching frequency justafter the lighting detection when the output power is smaller than thetarget value at the lighting detection by the lighting detection circuit14.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a circuit diagram showing a constitution of a conventionalexample.

FIG. 2 is a circuit diagram showing a constitution of a main part of aconventional example.

FIG. 3 is a chart showing characteristics of an oscillation frequency ofa conventional example.

FIG. 4 is a waveform chart for an explanation of an operation at astart-up of a conventional example.

FIG. 5 is a waveform chart for an explanation of an operation at astart-up of a conventional example.

FIG. 6 is a perspective view showing a fixture constitution for anexplanation of a problem of a conventional example.

FIG. 7 is a chart showing characteristics of resonance curve lines foran explanation of a problem of a conventional example.

FIG. 8 is a circuit diagram showing a constitution in an embodiment 1 ofthe present invention.

FIG. 9 is a chart showing resonance characteristics in the embodiment 1of the present invention.

FIG. 10 is an operational waveform chart in the embodiment 1 of thepresent invention.

FIG. 11 is a chart showing output characteristics for an explanation ofa problem of a conventional example.

FIG. 12 is a circuit diagram showing another example of a loadconstitution of the present invention.

FIG. 13 is a circuit diagram showing a constitution in an embodiment 2of the present invention.

FIG. 14 is a circuit diagram showing a constitution in an embodiment 3of the present invention.

FIG. 15 is an operational waveform chart in the embodiment 3 of thepresent invention.

FIG. 16 is a circuit diagram showing a constitution in an embodiment 4of the present invention.

FIG. 17 is a circuit diagram showing a constitution in an embodiment 5of the present invention.

FIG. 18 is an operational waveform chart in the embodiment 5 of thepresent invention.

FIG. 19 is an operational waveform chart in the embodiment 5 of thepresent invention.

FIG. 20 is a circuit diagram showing a constitution in an embodiment 6of the present invention.

FIG. 21 is an operational waveform chart in the embodiment 6 of thepresent invention.

FIG. 22 is an operational waveform chart in the embodiment 6 of thepresent invention.

FIG. 23 is a circuit diagram showing a constitution in an embodiment 7of the present invention.

FIG. 24 is an operational waveform chart in the embodiment 7 of thepresent invention.

FIG. 25 is an operational waveform chart in the embodiment 7 of thepresent invention.

FIG. 26 is a circuit diagram showing a constitution in an embodiment 8of the present invention.

FIG. 27 is a chart showing characteristics of resonance curve lines whenlighting in an embodiment 9 of the present invention.

FIG. 28 is a partial cross section front view of a street light in anembodiment 10 of the present invention.

FIG. 29 is a side view of a security light in the embodiment 10 of thepresent invention.

DESCRIPTION OF EMBODIMENTS

(Embodiment 1)

FIG. 8 shows a constitution of an embodiment 1. Explanations ofconstitutions, operations and effects similar to the conventionalexample are omitted. Differences from the conventional example (FIG. 1)are what the embodiment 1 includes a lighting detection circuit 14 fordetecting a lighting of the electrodeless discharge lamp 6, and aholding circuit 16 for immediately stopping a frequency sweep controland holding a switching frequency finv when the lighting of theelectrodeless discharge lamp 6 is detected by performing the frequencysweep control in the voltage controller 13, and does not include thevariable resistor VR. In addition, the ON/OFF state of the switch SW0 isswitched by a start signal Vst that is a trigger signal for starting thefrequency sweep. Moreover, the start signal Vst is also applied to thelighting detector 14.

The lighting detection circuit 14 includes a circuit for dividing,rectifying and smoothing the high-frequency voltage Vcoil, a capacitorC12 for holding the start signal Vst for a predetermined period to applya trigger for the frequency sweep control, an operational amplifier Q2for detecting a case that the high-frequency voltage Vcoil exceeds apredetermined value during the frequency sweep control, a switch SW1 forallowing the capacitor C12 to be discharged by receiving an output ofthe operational amplifier Q2, diodes D4 and D5 composing an OR gate, alogical inverter Q5 for inverting an input signal, and the like. Also,the holding circuit 16 includes the capacitor C1 and diodes D1 and D2.

The following are descriptions of operations with reference to FIGS. 8to 10. As shown in FIG. 9, there are four categorized operations inwhich A: the frequency sweep control, B: the lighting of theelectrodeless discharge lamp 6, C: holding the switching frequency finvjust after lighting, and D: controlling the switching frequency finv soas to be set the output power of the inverter 2 at a predeterminedvalue.

(Operations A and B)

According to FIG. 10, the switch SW0 is switched from the ON-state tothe OFF-state due to the shift of the start signal Vst from an H levelto an L level, followed by starting the frequency sweep control. Whilethe start signal Vst is in the H level (time t≦t1), the capacitor C12 isalso charged with a predetermined voltage, in which the voltage V(C12)is in the H level.

After the time t=t1, the high-frequency voltage Vcoil is graduallyincreased by the frequency sweep control. When the high-frequencyvoltage Vcoil exceeds a predetermined voltage Vth, the output voltageVout (Q2) of the operational amplifier Q2 is to be in the H level (timet=t2 to t3).

During the period from t1 to t2, the start signal Vst is in the L level.While, the voltage V(C12) keeps the H level due to a diode D3 for areverse-current prevention. As a result, a voltage Vd1, which is alogical disjunction of the voltage V(C12) and the voltage V(Q2), keepsthe H level during the period of the time t≦t3.

Note that, the charge in the capacitor C12 is discharged since theswitch SW1 is switched from the OFF-state to the ON-state due to theshift of the voltage V(Q2) from the L level to the H level, and thevoltage V(C12) is shifted from the H level to the L level. Moreover,when the high-frequency voltage Vcoil is decreased because of animpedance variation after the electrodeless discharge lamp 6 is lighted,it is possible to shift the voltage Vd1 from the H level to the L levelstarting from the point of the lighting of the electrodeless dischargelamp 6 by setting the output voltage V(Q2) of the operational amplifierQ2 to shift from the H level to the L level. Therefore, an outputvoltage Vd2 of the lighting detection circuit 14 is shifted from the Llevel to the H level due to the lighting of the electrodeless dischargelamp 6 by the function of the logical inverter Q5.

(Operation C)

Just after the lighting detection of the electrodeless discharge lamp 6by the lighting detection circuit 14, a potential at an anode terminalof the diode D1 becomes lower than that at a cathode terminal, and acharge from a dc power supply E1 to the capacitor C1 is stopped becauseof the shift of the voltage Vd2 from the L level to the H level. Then,the switching frequency finv just after the lighting detection ismaintained by keeping the voltage VC1 at both ends of the capacitor C1at an approximately constant value by the function of the diode D1 for areverse-current prevention.

(Operation D)

After the lighting detection of the electrodeless discharge lamp 6, theswitching frequency finv is controlled by the current controller 17 onlywhen the output power of the inverter 2 exceeds a predetermined value,thereby maintaining the output power at approximately constant value asthe predetermined value. When the output power of the inverter 2 is lessthan the predetermined value, the switching frequency finv just afterthe lighting detection is continuously maintained.

For instance, FIG. 11 shows a case without the current controller 17 dueto a property of the output power Wout of the inverter 2 with respect tothe switching frequency finv. When a temperature of theelectric-discharge lamp is lowered, the curve line may be shifted to alow-output side (in FIG. 11, an arrow indicated by a reference sign “a”shows a direction that the temperature of the electric-discharge lamp islowered). As a result, a range of the switching frequency over apredetermined output power (=Wtg) may become narrower or completelydisappear. Therefore, even when resulting in the output power Wout<Wtgjust after lighting because of the low temperature, it is possible tomaintain the output power at approximately constant value as thepredetermined value by lighting while keeping the switching frequencyfinv just after the lighting detection, followed by operating thefeedback control by the current controller 17 when resulting in theoutput power Wout>Wtg due to the increase of the temperature of theelectric-discharge lamp.

Due to the operations A to D described above, the effect capable ofstarting and lighting stably can be achieved even when the loadimpedance of the electric-discharge lamp is varied. Also, the advantageof omitting the variable resistor VR conventionally used for absorbingthe deviations can be achieved since an influence for the startoperation of the end point frequency fe in the frequency sweep controlis lessened by operating the above-mentioned control.

In addition, in the operations according to the embodiment 1, as shownin FIG. 12, the load 3 may be other electric-discharge lamps such as aconstruction including an electric-discharge lamp (fluorescent light) FLhaving filaments F1 and F2 and a capacitor C20, and the like, and canobtain the similar effect.

For convenience, the switching frequency finv to be held may be shiftedto the low frequency side within a harmless range if it is adjacent tothe switching frequency finv just after the lighting detection.

(Embodiment 2)

FIG. 13 shows a constitution of an embodiment 2. Explanations ofconstitutions, operations and effects similar to the embodiment 1 areomitted. A difference from the embodiment 1 is what the holding circuit16 stores the switching frequency finv just after the lighting asdigital data. Also, the holding circuit 16 includes a microprocessor(MPU) 19, a memory 18, an A/D converter 21 for converting an analogvoltage into digital data, a D/A converter 20 for converting digitaldata into an analog voltage, and the like.

The following are descriptions of operations. The output voltage Vd2 ofthe lighting detection circuit 14 is shifted from the L level to the Hlevel due to the lighting of the electrodeless discharge lamp 6. Bytreating it as a trigger, the voltage VC1 at both ends of the capacitorC1 is stored and held in the memory 18 as digital data via the A/Dconverter 21 by the function of the MPU 19. Then, the stored data isreconverted into the analog voltage value via the D/A converter 20,followed by applying to the capacitor Cl. That means it is possible tomaintain the voltage VC1 at both ends of the capacitor Cl at the voltagevalue just after lighting, which means maintaining the switchingfrequency finv at the point. Compared with the case of the embodiment 1(maintaining at the analog voltage value at both ends of the capacitorC1), the effect capable of holding for a longer period can be achieved.

(Embodiment 3)

FIG. 14 shows a constitution of an embodiment 3. Explanations ofconstitutions, operations and effects similar to the embodiment 2 areomitted. A difference from the embodiment 2 is what an oscillator 24, abinary counter 22 (e.g. CMOS IC: 4024), a D/A converter 23, and the likeare used as the holding circuit 16. The oscillator 24 includes a Schmitttrigger logical inverter Q10 (e.g. CMOS IC: 74HC14), a capacitor C13,and the resistor R11. By use of hysteresis characteristics of an inputthreshold voltage of the Schmitt trigger logical inverter Q10, a squarewave voltage oscillation is performed. An oscillation frequency isdetermined by a time constant of the capacitor C13 and the resistor R11,and a hysteresis width.

The following are descriptions of operations with reference to FIG. 15.Due to a shift of the start signal Vst from the H level to the L level(time t=t1), a reset of the binary counter 22 is released, and an outputvoltage Vosc of the oscillator 24 is applied to the binary counter 22,followed by starting counting operation. The output of the binarycounter 22 is converted into an analog voltage via the D/A converter 23and the capacitor C1. Then, the frequency sweep is operated by graduallyincreasing the voltage VC1.

The output voltage Vd2 of the lighting detection circuit 14 is shiftedfrom the L level to the H level due to the lighting of the electrodelessdischarge lamp 6. By treating it as a trigger, the switch SW0 is shiftedfrom the OFF-state to the ON-state, and the oscillation of theoscillator 24 is stopped. As a result, the output voltage of the D/Aconverter 23 is held since the counting operation is stopped. Thus, itis possible to maintain the voltage VC1 at both ends of the capacitor Clat the voltage value just after lighting, which means maintaining theswitching frequency finv at the point. That means the voltage value isheld as digital data by the binary counter 22 according to the presentembodiment.

In the present embodiment, there is the advantage of operability at lowcost using only general-purpose components without the MPU 19 comparedwith the embodiment 2.

(Embodiment 4)

FIG. 16 shows a constitution of an embodiment 4. Explanations ofconstitutions, operations and effects similar to the embodiment 1 areomitted. A difference from the circuit in the embodiment 1 (FIG. 8) iswhat the lighting detection circuit 14 inputs the detected voltage ofthe output voltage Vcoil into an inverting terminal of the operationalamplifier Q1 of the voltage controller 13. Therefore, by operating thefeedback control to comply a voltage value variation of a non-invertingterminal of the operational amplifier Q1, the frequency sweep is to becontrolled so as to approach a certain target value. Thus, the effectcapable of starting stably can be achieved since an excess of the outputvoltage Vcoil and the like can be prevented due to a gradual start-up ofthe output voltage Vcoil even when a resonance property at the startingof the electrodeless discharge lamp 6 in the oscillator including theinverter 2 and the load 3 is tilted steeply.

(Embodiment 5)

FIG. 17 shows a constitution of an embodiment 5. Explanations ofconstitutions, operations and effects similar to the embodiment 4 areomitted. Differences from the circuit in the embodiment 4 (FIG. 16) arewhat the present embodiment is configured to input the dc voltage E1divided by the resistors R1, R21 and R22 into the non-inverting terminal(voltage V+) of the operational amplifier Q1 in the voltage controller13, include the holding circuit 16 including the resistor R22 and theswitch SW1, and decrease the voltage V+ by being conducted through theswitch SW1 connected in parallel to the resistor R22 when the lightingis detected by the lighting detection circuit 14.

FIGS. 18 and 19 show operational waveform charts. In general, a voltageV− of the inverting terminal of the operational amplifier Q1, which is adivided voltage of the output voltage Vcoil, is decreased by theimpedance variation after the electrodeless discharge lamp 6 is lighted.Thus, the voltage V− becomes relatively smaller than the voltage V+,thereby increasing an output voltage Vf of the operational amplifier Q1again. However, when the impedance variation is occurred, e.g. when themetal housing approaches the electrodeless discharge lamp 6, the endpoint frequency fe of the frequency sweep may become lower than the peakof the resonance curve line when lighting (refer to FIGS. 4 and 7).

In the present embodiment, it is possible to hold the voltage Vf, andmaintain the switching frequency finv at the value just after lightingby decreasing the voltage V+ by turning on the switch SW1 in order tocomply the voltage variation of the voltage V− after the electrodelessdischarge lamp 6 is lighted. Therefore, the effect capable of startingand lighting stably can be achieved even when operating the feedbackcontrol for the output voltage Vcoil.

(Embodiment 6)

FIG. 20 shows a constitution of an embodiment 6. Explanations ofconstitutions, operations and effects similar to the embodiment 5 areomitted. A difference from the circuit in the embodiment 5 (FIG. 17) iswhat the present embodiment includes the holding circuit 16 that appliesa voltage to the inverting terminal of the operational amplifier Q1 byreceiving the output from the lighting detection circuit 14, andincludes an operational amplifier Q7, a resistor, and a diode.

FIGS. 21 and 22 show operational waveform charts. It is possible to holdthe voltage Vf, and maintain the switching frequency finv at the valuejust after lighting similar to the embodiment 5 by increasing thevoltage V− via the holding circuit 16, in order to comply the voltagevariation of the voltage V+ after the electrodeless discharge lamp 6 islighted. In addition, the effect similar to the embodiment 5 can beachieved.

(Embodiment 7)

FIG. 23 shows a constitution of an embodiment 7. Explanations ofconstitutions, operations and effects similar to the embodiment 5 areomitted. A difference from the circuit in the embodiment 5 (FIG. 17) iswhat the present embodiment includes the holding circuit 16 thatextracts a current (Iig) from the input terminal of the drive circuit 11by receiving the input from the lighting detection circuit 14, andincludes a logical inverter Q8, a capacitor, and a resistor.

FIGS. 24 and 25 show operational waveform charts. It is possible toequivalently hold the voltage Vf, i.e. maintain the switching frequencyfinv at the value just after lighting, by shifting the output of thelogical inverter Q8 from the H level to the L level, and extracting thecurrent Iig from the holding circuit 16 to supplement the decrease ofthe current Isw caused by the difference between the voltages V+ and V−after the electrodeless discharge lamp 6 is lighted. Thus, the similareffect can be achieved.

(Embodiment 8)

FIG. 26 shows a constitution of an embodiment 8. Explanations ofconstitutions, operations and effects similar to the embodiment 5 areomitted. A difference from the circuit in the embodiment 5 (FIG. 17) iswhat the voltage controller 13 includes the MPU 19, the memory 18, theA/D converter 21 for converting an analog voltage into digital data, theD/A converter 20 for converting digital data into an analog voltage, andthe like. An input port I_1 of the MPU 19 determines an H/L status ofthe start signal Vst, and an input port I_2 determines an H/L status ofthe output signal Vd2 of the lighting detection circuit 14. The dividedvoltage of the output voltage Vcoil is converted into digital data viathe A/D converter 21 and inputted into the MPU 19, and the output fromthe MPU 19 is outputted into the drive circuit 11 as an analog voltagevalue via the D/A converter 20. The function of the current controller17 provided in the embodiment 5, which controls the switching frequencyso as to maintain the output power of the electrodeless discharge lamp 6at an approximately constant target value, is combined with the voltagecontroller 13. Thus, the similar operations can be performed by use ofthe MPU 19. Also, the effect capable of more easily and accuratelymaintaining the switching frequency finv at the value just afterlighting can be achieved compared with the case using analog componentssuch as an operational amplifier, and the advantage of reducing thenumber of components can be obtained. Note that, the function of thelighting detection circuit 14 may be combined with the voltagecontroller 13, which achieves the further reduction of the number ofcomponents.

(Embodiment 9)

The present embodiment includes the electrodeless discharge lamp 6according to each embodiment 1 to 8, in which at least one of the buffergases including Kr.

FIG. 27 shows resonance curve lines when the electrodeless dischargelamp 6 is lighted. When Kr is used as an inactive gas to be filled inthe electrodeless discharge lamp 6, the load impedance is lowered more,and the resonance curve line can be broader compared with the case usingAr. Thus, the effect capable of reducing a sensitivity of the outputpower with respect to the switching frequency, and the effect capable ofmore accurately and stably performing the respective operationsdescribed in the above-mentioned embodiments 1 to 8, can be achieved.

(Embodiment 10)

The electric-discharge lamp lighting devices according to theembodiments 1 to 9 can be widely used for lighting fixtures such as astreet light 35 in FIG. 28, a security light 36 in FIG. 29, or adownlight (FIG. 6), and the effects similar to the above-describedrespective embodiments can be obtained.

Industrial Applicability

According to the present invention, the first frequency controllerincludes a holding means that holds the switching frequency just afterthe lighting detection when the output power is smaller than a targetvalue at the lighting detection. Therefore, the effect capable of stablystarting and lighting can be achieved even when the load impedance ofthe electric-discharge lamp is varied.

1. An electric-discharge lamp lighting device, comprising: a power inverter configured to output an AC voltage by receiving electric power from a DC power supply and including at least a switching element and a resonant circuit; a drive circuit configured to drive the switching element; a load connected to an output of the power inverter and connected to at least an electric-discharge lamp; a first frequency controller configured to sweep a switching frequency of the drive circuit so that the output of the power inverter is gradually increased in order to allow the electric-discharge lamp to be started and lit; a second frequency controller configured to detect an output power of the power inverter by a current flowing in the resonant circuit and to control the switching frequency of the drive circuit so that the output power is set to be a target value after the discharge lamp is started and lit; and a lighting detector configured to perform a lighting detection of the electric-discharge lamp by detecting the output of the power inverter, wherein the first frequency controller includes a holding circuit configured to hold the switching frequency just after the lighting detection, when the output power is smaller than the target value at the lighting detection by the lighting detector, and the second frequency controller controls the switching frequency to maintain the output power at a substantially constant value, as the target value, after the output power reaches the target value.
 2. The electric-discharge lamp lighting device of claim 1, wherein the holding circuit holds the switching frequency just after the lighting detection by a digital storage element.
 3. The electric-discharge lamp lighting device of claim 1, wherein the lighting detector performs the lighting detection of the electric-discharge lamp by detecting a reduction of the output of the power inverter.
 4. The electric-discharge lamp lighting device of claim 1, wherein the first frequency controller detects the output of the power inverter and sweeps the switching frequency so as to be a target output by a feedback control.
 5. The electric-discharge lamp lighting device of claim 4, wherein the first frequency controller includes a differential amplifier configured to perform differential amplification of a detection value of the output of the power inverter and a target value for the target output, in order to perform the feedback control, and the first frequency controller controls the switching frequency of the drive circuit according to an output of the differential amplifier, and the holding circuit holds the output of the differential amplifier so that the switching frequency at the lighting detection is held.
 6. The electric-discharge lamp lighting device of claim 5, wherein the holding circuit holds the output of the differential amplifier by varying the target value.
 7. The electric-discharge lamp lighting device of claim 5, wherein the holding circuit holds the output of the differential amplifier by varying the detection value.
 8. The electric-discharge lamp lighting device of claim 4, wherein the first frequency controller includes a differential amplifier configured to perform differential amplification of a detection value of the output of the power inverter and a target value for the target output, in order to perform the feedback control, and the first frequency controller controls the switching frequency of the drive circuit according to an output of the differential amplifier and an output of the lighting detector, and the holding circuit varies the output of the lighting detector so that the switching frequency at the lighting detection is held.
 9. The electric-discharge lamp lighting device of claim 1, wherein the electric-discharge lamp includes at least one of buffer gases including Kr.
 10. The electric-discharge lamp lighting device of claim 1, wherein the load includes an induction coil connected to the output of the power inverter and an electrodeless discharge lamp including a bulb to light provided adjacent to the induction coil and filled with discharge gas.
 11. A lighting fixture, comprising: the electric-discharge lamp lighting device of claim
 1. 